Author Topic: BZ 500MPPT assembly issues  (Read 431 times)

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dnix71

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BZ 500MPPT assembly issues
« on: January 29, 2013, 06:30:08 PM »
I have a BZ MPPT 250 and an MPPT 500. The 250 was assembled with too-short circuit board standoffs and failed after 3 days. BZ promptly replaced the unit and the retailer was notified and pulled his stock and sent it back for rework.

My 500 is a couple of years old now. It has always reported the battery voltage on the display as being much higher than it really is when the unit is charging, but is accurate at rest. That forced me to set the float cutoff near the max to avoid the unit cutting back on charging when the battery was nowhere near full. This behavior has gotten worse with age.

The 250 is on a panel mount so it's easy to see the front and back of the board. The 500 is in a box with the FETs heat sinked to the back of the box. Since I figure I got my money's worth from the 500 and had a week off from work, I took the 500 apart to see if I could tell what was causing the voltage reading discrepancy.

The caps look okay but I don't have an ESR meter to check them.

The panel negative and battery negative are bridged on the back side of the board by two short wires that are soldered to the same spot. Thinking that the wires might simply be too thin I added soldered an extra wire over each and reassmbled the 500.

This "fix" made no improvement and actually seemed to make it worse in bright sun. So I took the 500 apart again and removed the wires.

Looking over the board carefully I noticed the ring toroid with 3 separate wires (which is visible when you remove the enclosure cover) is in the main positive output trace. It's probably an RF choke. Earlier BZ models were noted for interfering with CB radio. I have portable radios very near this unit and have never heard any noise from it.

Looking at the back of the board where the toroid was mounted I noticed the three wires were stripped of varnish at the end and tinned before inserting them through the board and soldered. The cut ends, however stuck out in the air because there wasn't enough solder on that pad to submerge the ends. I added a pool of solder over the pad until the ends were covered and reassmbled the 500. It still reads a bit high under bright sun but the difference is much smaller.

I also added clip on CB ferrites to the positive wires (panel and battery).

If you have a BZ 500 and it reads high when charging it might be worth the time to tae it apart and add some solder to the back side of that choke coil.

boB

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Re: BZ 500MPPT assembly issues
« Reply #1 on: January 29, 2013, 07:25:21 PM »
If it really did read better after disassembling and reassembling,  maybe it could also have
been something else in there that you jarred while moving its insides around ?

Kind of like when you smack the side of a TV set to get it to work right.

Or maybe it was just what you did by resoldering that wire.

You might try smacking it lightly to see if the voltage reading moves around while
doing that just to make sure.

boB

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #2 on: January 29, 2013, 07:36:14 PM »
The voltage reads right when there is no incoming current. I bright sun it would jump up 2 volts. Nothing is loose. The controller is 2 stage. There is a relay to switch 2 FETs, but the voltage jump was occurring without the second stage in play.

ChrisOlson

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Re: BZ 500MPPT assembly issues
« Reply #3 on: January 29, 2013, 09:11:37 PM »
My MPPT500 did that too, to a certain extent.  But never 2 volts.  Maybe about .3 volts high on an average day and up to .4 or .5 volts on a good day.  But my Classics do that too.  They read the right voltage at rest and a couple tenths high during full power charging.  But with 60-70 amps flowing thru #4 THHN that's to be expected.
--
Chris

boB

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Re: BZ 500MPPT assembly issues
« Reply #4 on: January 29, 2013, 10:50:53 PM »
The voltage reads right when there is no incoming current. I bright sun it would jump up 2 volts. Nothing is loose. The controller is 2 stage. There is a relay to switch 2 FETs, but the voltage jump was occurring without the second stage in play.

Where is your external meter measuring that voltage ?   At the battery terminals ?  Terminals of the BZ controller ?

Sounds like the BZ's voltage sample point is not quite at the BZ's terminals but somewhat inside
the controller.  That makes sense then that your soldering job helped it out.  2.0 volts is a LOT
though !  For any decent amount of battery current, that would make one hot connection at
the weak point !

boB

OperaHouse

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Re: BZ 500MPPT assembly issues
« Reply #5 on: January 30, 2013, 07:17:50 AM »
How about posting a picture.  Form follows function and with a picture would give me a good idea of what the schematic would be.  Resistance between the battery and the sampling point would cause this.  Either in wiring or in the unit.  Another problem would be the nois filtering on the sample line.  The micro may be reading spikes.  An additional small resistor and cap in the sampling line may fix this. This may be the problem as the batteries begin to sulfate.

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #6 on: January 30, 2013, 10:19:08 AM »
I can post a pic of the front when I get home. The voltage at the terminal blocks and battery posts is the same. The wire between the two is short. One BZ may be seeing the other since both are in parallel to charge the batteries. I have too much panel for either. I kept adding panels until I needed a second controller. The 2 controllers each have their own set of panels but because the controllers internally bridge the PV negative to battery ground, both sets of panels share a common negative.

OperaHouse

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Re: BZ 500MPPT assembly issues
« Reply #7 on: January 30, 2013, 11:53:21 AM »
That kind of picture wouldn't do much good.  If you have a large capacitor with screw terminals and place it at the BZ that might help. 

MaryAlana

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Re: BZ 500MPPT assembly issues
« Reply #8 on: January 30, 2013, 12:06:36 PM »
By taking it apart and reassembling it you may have fixed a bad ground at a screw hole.

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #9 on: January 30, 2013, 12:36:48 PM »
One of the four standoffs is a circuit board ground. I double checked that on reassembly and added a housing to battery ground wire. I've tried the large capacitor trick but it prevents the logic circuit from locking. The voltage and current oscillate forever with a 12k uF cap across the PV. I haven't tried that on the battery side, though. That's worth trying one day when I'm home during midday and can watch what happens.

The cap trick keeps the smaller BZ from switching off and on so much during low light. That wakes me up in the morning. Click - click - click -click. The larger BZ only switches after there is a certain medium power on it, not in low light.

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #10 on: January 30, 2013, 04:27:09 PM »
Here are the pics






OperaHouse

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Re: BZ 500MPPT assembly issues
« Reply #11 on: January 31, 2013, 10:41:54 AM »
Good picture.  The three large electrolytics appear to be on the panel side.  I wouldn't expect much change id another cap was paralleled on the input side unless these had developed a high ESR over the years.  The small cap appears to be on the output with the expectation that the battery would take most of the surge.  The large coil would normally have three or four parallel windings for practical reasons in order to handle the current.  The coil next to it is the switching regulator for the microprocessor power.  ust curious what that white thing with the green stripes.  Probably just a production tag.  It made me think of a product where they put a resistor on top of the micro to heat it up just to qualify it for low temperature operation.  Looks like 3 FET to do the comversion and two tabbed dioded.  I would guess that the relay is used to disconnect panels at night.  Again a regulator and coil to power the relay over a wide voltage range.

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #12 on: January 31, 2013, 03:50:27 PM »
The green and white thing is a paper tag on a chip. Years ago BZ offered a firmware upgrade in the form of a chip replacement. I was never offered that so I probably have the latest version.

There are four power FETs. 2 up and 2 down. Those are isolated from the box with a plastic shim under the heat sink and the screws are plastic. The fifth FET (the one at the bottom) is a voltage regulator that supplies some components on the board.
There are plastic standoffs on a couple of the FET legs to guarantee no shorts.

There are 3 winding on the big coil.

Now that I've added solder to the back side I'm getting a much better charge during the day, even today when I came home it was 13.0 and it was overcast and had rained as a cool front passed.

captainward

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Re: BZ 500MPPT assembly issues
« Reply #13 on: February 19, 2014, 12:01:59 AM »
I have one of these bz 500 my only complaint is the float light won't come on seems to keep all the batterys charged properly up to about 13 volts. but when it gets the batts up to full charge no red led light????
                 anyone know how to fix the red light issue??  Thanks for l@@king.

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #14 on: February 19, 2014, 08:21:31 AM »
CaptainWard 13 volts is not a full charge. Somewhere around 14 to 15 is. Either your BZ has failed or you don't have it wired correctly. I would contact BZ first. They were nice to me about fixing issues. If the controller has gone bad they might give you a partial credit on a replacement in exchange for the old one if you ask nice.

My two BZ's (a 250 and a 500HV still work well in daily use).

boB

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Re: BZ 500MPPT assembly issues
« Reply #15 on: February 19, 2014, 02:13:19 PM »

I had heard that the BZ does not actually go to Float ?  Is this true ?

If it were to just stay in Absorb all day long at the highest regulated voltage, this would not be good.

Were the rumors true or false ?  If it actually has a Float LED, I would think it would intend to go to
Float after some amount of time in Absorb.

boB

dnix71

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Re: BZ 500MPPT assembly issues
« Reply #16 on: February 19, 2014, 02:52:07 PM »
I don't know if my BZ is three stage, but it most definitely has a float. It also has a two-stage charging circuit. Near the float voltage it backs off charging. The float light will flicker, but if there is lots of sun, it will go hard red and sit there until either the batteries voltage drops from a load or the sun goes down.

The final voltage is adjustable so it shouldn't matter what kind of battery you have. You can set it to cut off in the low 13's, or florce it as high as about 15.5.